Gas turbine engine airfoil

ABSTRACT

An airfoil includes pressure and suction sides that extend between a leading edge and a trailing edge. The airfoil has a camber line along an airfoil section that is equidistant between the exterior surface of the pressure and suction sides. The camber line extends from a 0% camber position at the leading edge to a 100% camber position at the trailing edge. A ratio of a maximum thickness to an axial chord length is between 0.2 and 0.5. The maximum thickness is located along the camber line between about 13% and 38% camber position.

BACKGROUND

This disclosure relates to gas turbine engine airfoils. Moreparticularly the disclosure relates to normalized airfoil thickness andpressure side curvature characteristics so as to enable the airfoil tobe tolerant of high degrees of incidence variation.

A turbine engine such as a gas turbine engine typically includes a fansection, a compressor section, a combustor section and a turbinesection. Air entering the compressor section is compressed and deliveredinto the combustor section where it is mixed with fuel and ignited togenerate high-temperature gas flow. The high-temperature gas flowexpands through the turbine section to drive the compressor and the fansection. The compressor section typically includes at least low and highpressure compressors, and the turbine section typically includes atleast low and high pressure turbines. In some applications, a powerturbine further expands the flow to drive one or more components whichare not a part of the gas turbine engine.

Direct drive gas turbine engines include a fan section that is drivendirectly by one of the turbine shafts. Rotor blades in the fan sectionand sometimes a low pressure compressor of the compressor section ofdirect drive engines rotate in the same direction. Geared gas turbineengines have a geared architecture arranged between the fan section andthe turbine section. The geared architecture enables the associatedcompressor of the compressor section to be driven at differentrotational speeds than the turbine generating the power for theparticular compressor.

The aerodynamics within the turbine section may result in the airfoilsseeing a significant change in incidence. This variation in incidencepresents design challenges.

SUMMARY

In one exemplary embodiment, an airfoil includes pressure and suctionsides that extend between a leading edge and a trailing edge. Theairfoil has a camber line along an airfoil section that is equidistantbetween the exterior surface of the pressure and suction sides. Thecamber line extends from a 0% camber position at the leading edge to a100% camber position at the trailing edge. A ratio of a maximumthickness to an axial chord length is between 0.2 and 0.5. The maximumthickness is located along the camber line between about 13% and 38%camber position.

In a further embodiment of any of the above, the pressure and suctionsides extend in a radial direction from a 0% span position to a 100%span position. The airfoil section is between 5% and 95% span.

In a further embodiment of any of the above, a thickness of the airfoilas a percentage of the maximum thickness is between about 28% and about76% at a 5% camber position.

In a further embodiment of any of the above, a thickness of the airfoilas a percentage of the maximum thickness is between about 4% and about20% at a 95% camber position.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by the axial chord length of between −1 and−3 at about a 46% axial position.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by the axial chord length of between 1.6 and5.2 at about a 5% axial position.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by the axial chord length of between −0.1and −1.6 at about a 95% axial position.

In a further embodiment of any of the above, a thickness of the airfoilas a percentage of the maximum thickness over the camber position iswithin a first and a second thickness trend line as shown in FIG. 5.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by a chord length over the axial chordposition within a first and a second curvature trend line as shown inFIG. 6.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by a chord length over the axial chordposition within a first and a second curvature trend line as shown inFIG. 6.

In another exemplary embodiment, a gas turbine engine includes acombustor section arranged between a compressor section and a turbinesection. An airfoil is arranged in one of the compressor section and theturbine section. The airfoil has pressure and suction sides that extendbetween a leading edge and a trailing edge. The airfoil has a camberline along an airfoil section that is equidistant between the exteriorsurface of the pressure and suction sides. The camber line extends froma 0% camber position at the leading edge to a 100% camber position atthe trailing edge. A ratio of a maximum thickness to an axial chordlength is between 0.2 and 0.5. The maximum thickness is located alongthe camber line between about 13% and 38% camber position.

In a further embodiment of any of the above, the airfoil is a statorairfoil.

In a further embodiment of any of the above, the airfoil is a rotorairfoil.

In a further embodiment of any of the above, the airfoil is arranged inthe turbine section.

In a further embodiment of any of the above, a thickness of the airfoilas a percentage of the maximum thickness is between about 28% and about76% at a 5% camber position. The thickness of the airfoil as apercentage of the maximum thickness is between about 4% and about 20% ata 95% camber position.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by the axial chord length of between 1.6 and5.2 at about a 5% axial position. The radius of curvature is divided bythe axial chord length of between −0.1 and −1.6 at about a 95% axialposition

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by the axial chord length of between −1 and−3 at about a 46% axial position.

In a further embodiment of any of the above, a thickness of the airfoilas a percentage of the maximum thickness over the camber position iswithin a first and a second thickness trend line as shown in FIG. 5.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by a chord length over the axial chordposition within a first and a second curvature trend line as shown inFIG. 6.

In a further embodiment of any of the above, the pressure side has aradius of curvature divided by a chord length over the axial chordposition within a first and a second curvature trend line as shown inFIG. 6.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 schematically illustrates an exemplary gas turbine engine.

FIG. 2A is a schematic view of airfoil span positions for an exampleairfoil.

FIG. 2B is a schematic view of airfoil span positions for anotherexample airfoil.

FIG. 3 is a schematic view of a cross-section of an airfoil sectioned ata particular span position and depicting directional indicators.

FIG. 4 is a schematic view of an airfoil depicting mean camber of theairfoil.

FIG. 5 graphically depicts a curve of an example airfoil thickness tocamber position.

FIG. 6 graphically depicts a curve of an example airfoil pressure sidecurvature to turbine centerline, or axial position.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following description and drawings, including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct defined within a housing15 such as a fan case or nacelle, and also drives air along a core flowpath C for compression and communication into the combustor section 26then expansion through the turbine section 28. Although depicted as atwo-spool turbofan gas turbine engine in the disclosed non-limitingembodiment, it should be understood that the concepts described hereinare not limited to use with two-spool turbofans as the teachings may beapplied to other types of turbine engines including three-spool turbofanarchitectures, turbojet, turboramjet, turboprob, or turboshaft engines.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects, a first (or low) pressure compressor 44 and a first (orlow) pressure turbine 46. The inner shaft 40 is connected to the fan 42through a speed change mechanism, which in exemplary gas turbine engine20 is illustrated as a geared architecture 48 to drive a fan 42 at alower speed than the low speed spool 30. The high speed spool 32includes an outer shaft 50 that interconnects a second (or high)pressure compressor 52 and a second (or high) pressure turbine 54. Acombustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 may be arranged generallybetween the high pressure turbine 54 and the low pressure turbine 46.The mid-turbine frame 57 further supports bearing systems 38 in theturbine section 28. The inner shaft 40 and the outer shaft 50 areconcentric and rotate via bearing systems 38 about the engine centrallongitudinal axis A which is collinear with their longitudinal axes. Insome applications, a power turbine further expands the flow to drive oneor more components which are not a part of the gas turbine engine.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. Although depicted with a mid-turbineframe in the gas turbine engine in the disclosed non-limitingembodiment, it should be understood that the concepts described hereinare not limited to an architecture featuring a mid-turbine frame. Theturbines 46, 54 rotationally drive the respective low speed spool 30 andhigh speed spool 32 in response to the expansion. It will be appreciatedthat each of the positions of the fan section 22, compressor section 24,combustor section 26, turbine section 28, and fan drive gear system 48may be varied. For example, gear system 48 may be located aft of the lowpressure compressor, or aft of the combustor section 26 or even aft ofturbine section 28, and fan 42 may be positioned forward or aft of thelocation of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1 and less than about 5:1. Itshould be understood, however, that the above parameters are onlyexemplary of one embodiment of a geared architecture engine and that thepresent invention is applicable to other gas turbine engines includingdirect drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and35,000 ft (10,668 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (‘TSFC’)”—is the industry standard parameter of lbm of fuelbeing burned divided by lbf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]^(0.5). The “Lowcorrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second (350.5meters/second).

FIGS. 2A and 2B illustrate an example airfoil 64. The airfoil 64 may bea turbine vane or blade, for example. Span positions on an airfoil 64are schematically illustrated from 0% to 100% in 10% increments. Eachsection at a given span position is oriented in an aerodynamicallyrelevant fashion, which can be either a conical cut that corresponds tothe shape of the core flow path, as shown by the large dashed lines inFIG. 2A, or some other aerodynamically relevant section cut, forexample, at constant radii, as shown by the large dashed lines in FIG.2B. In some examples, the airfoil 64 has an integral platform. In thecase of an airfoil with an integral platform, the 0% span positioncorresponds to the radially innermost location where the airfoil meetsthe fillet joining the airfoil to the inner platform. In the case of anairfoil without an integral platform, the 0% span position correspondsto the radially innermost location where the discrete platform meets theexterior surface of the airfoil. For airfoils having no outer platform,such as unshrouded blades, the 100% span position corresponds to the tip66. For airfoils having no platform at the inner diameter, such ascantilevered stators, the 0% span position corresponds to the innerdiameter location of the airfoil. For stators, the 100% span positioncorresponds to the outermost location where the airfoil meets the filletjoining the airfoil to the outer platform.

Referring to FIG. 3, and with continued reference to FIGS. 2A and 2B,airfoils are specifically designed radially from an inner airfoillocation (0% span) to an outer airfoil location (100% span) and alongcircumferentially opposite pressure and suction sides 72, 74 extendingin chord between a leading and trailing edges 68, 70. Each airfoil isspecifically designed with a particular thickness and curvature alongthe airfoil. Airfoil geometric shapes, stacking offsets, chord profiles,stagger angles, sweep and dihedral angles, among other associatedfeatures, are incorporated individually or collectively to improvecharacteristics such as aerodynamic efficiency, structural integrity,and vibration mitigation, for example, in a gas turbine engine.

The airfoil 64 has an exterior surface 76 providing a contour thatextends from a leading edge 68 generally aftward in a chord-wisedirection H to a trailing edge 70, as shown in FIG. 3. Pressure andsuction sides 72, 74 join one another at the leading and trailing edges68, 70 and are spaced apart from one another in an airfoil thicknessdirection T. An array of airfoils 64 are positioned about the axis X(corresponding to the turbine center line direction) in acircumferential or tangential direction Y. Any suitable number ofairfoils may be used for a particular stage in a given engineapplication.

The exterior surface 76 of the airfoil 64 generates lift based upon itsgeometry and directs flow along the core flow path C. The airfoil 64 maybe constructed from any composite material, aluminum alloy, titaniumalloy, nickel alloy or super-alloy, iron alloy or a combination of oneor more of these. Abrasion-resistant coatings or other protectivecoatings may be applied to the airfoil. Furthermore, the airfoil may besolid or cored for cooling or weight reduction purposes, and may or maynot feature film cooling. The rotor stages may be constructed as anintegrally bladed rotor, if desired, or discrete blades having rootssecured within corresponding rotor slots of a disc. The stators may beprovided by individual vanes, clusters of vanes, or a full ring ofvanes.

Airfoil geometries can be described with respect to various parametersprovided. The disclosed graph(s) illustrate the relationships betweenthe referenced parameters within 5% of the desired values, whichcorrespond to a cold aerodynamic design for the airfoil, so as to enablephysical inspection. It should be understood that the airfoils may beoriented differently than depicted, depending on the rotationaldirection of the blades. The signs (positive or negative) used, if any,in the graphs of this disclosure are controlling and the drawings shouldthen be understood as a schematic representation of one example airfoilif inconsistent with the graphs. The signs in this disclosure, includingany graphs, comply with the “right hand rule.”

FIG. 4 shows an example airfoil section 65 of the airfoil 64. As shown,the airfoil 64 is sectioned at a radial position between the root andthe tip. The airfoil section 65 may be between about the 5% and 95% spanpositions. In a further embodiment, the airfoil section 65 may bebetween about the 25% and 75% span positions. A camber mean line ML lieswithin the airfoil section and is equidistant between the exteriorsurface of the pressure and suction sides 72, 74. Camber positions onthe airfoil 64 are schematically illustrated from 0% to 100%. The cambermean line ML intersects the leading edge 68 at a 0% camber position, andintersects the trailing edge 70 at a 100% camber position. An axialchord CL of the airfoil section 65 is a straight line along the turbinecenter line axis X that extends from a most upstream location 69 to theturbine centerline at a most downstream location 71 on the airfoilsurface 76. A normalized axial position is the position along the axialchord CL divided by the axial chord length. Normalized axial positionson the airfoil 64 are schematically illustrated from 0 to 1. The axialchord CL intersects the turbine centerline most upstream location 69 ata 0 axial position, and intersects the turbine centerline mostdownstream location 71 at a 1 axial position.

An airfoil thickness 78 is defined as the distance between the pressureand suction sides 72, 74 normal to the camber mean line ML. The airfoil64 has a maximum thickness between the leading and trailing edges 68,70. A ratio of the maximum thickness to the axial chord length isbetween 0.2 and 0.5. The specified parameter enables the communicationof a distinct normalized shape, which has characteristics that enable anincident tolerant geometry for high levels of positive or negativeincidence. For geometries outside of the specified bounds, and with highlevels of positive or negative incidence, undesirable aerodynamiccharacteristics are encountered. The pressure side 72 has a radius ofcurvature that varies between the leading and trailing edge 68, 70.

FIG. 5 illustrates the airfoil thickness 78 over the camber position foran airfoil section 65. The thickness 78 is shown as a percentage of themaximum thickness. That is, the thickness on the y-axis is the airfoilthickness as a percentage of the maximum thickness in the airfoilsection 65. The graph depicts a first thickness trend line 80 and asecond thickness trend line 82. The airfoil thickness 78 is between thefirst and second thickness trend lines 80, 82 along the camber positionof the airfoil section 65. The maximum thickness may be located betweenabout 13% and 38% camber position. The airfoil section has a thicknessbetween about 28% and about 76% at a 5% camber position. The airfoilsection has a thickness between about 4% and about 20% at 95% camberposition.

FIG. 6 illustrates the pressure side curvature over the turbine axial(relative to turbine centerline) position for an airfoil section. Thegraph depicts a first curvature trend line 90 and a second curvaturetrend line 92. The pressure side curvature is between the first andsecond curvature trend lines 90, 92 along the turbine axial position ofthe airfoil section 65. The first curvature trend line 90 has a firstportion 94 and a second portion 96. The second curvature trend line 92has a first portion 98 and a second portion 100. The first portions 94,98 generally have a negative slope, while the second portions 96, 100have a positive slope. The first portions 94, 98 may have a steeperslope than the second portions 96, 100. The first portions 94, 98 andthe second portions 96, 100 meet at a point 95, 99, respectively. Thepoint 95, 99 may be at about the 46% axial position. The pressure sideradius of curvature divided by a chord length may be between −1 and −3at about the 46% axial position. The radius of curvature divided by achord length may be between 1.6 and 5.2 at about a 5% axial position.The radius of curvature divided by a chord length may be between −0.1and −1.6 at about a 95% axial position. The specified parameters enablethe communication of a distinct normalized shape, which hascharacteristics that enable an incident tolerant geometry for highlevels of positive or negative incidence. For geometries outside of thespecified bounds, and with high levels of positive or negativeincidence, undesirable aerodynamic characteristics are encountered.

For turbines that are required to operate at high efficiency over a widerange of speeds or pressure ratios, the airfoils can see significantchanges in incidence. The magnitude of the change in incidence is afunction of the turbine operating range. The disclosed airfoil providesa unique aerodynamic design that may perform well under high levels ofpositive or negative incidence. The specified parameters enable thecommunication of a distinct normalized shape, which has characteristicsthat enable an incident tolerant geometry for high levels of positive ornegative incidence. For geometries outside of the specified bounds, andwith high levels of positive or negative incidence, undesirableaerodynamic characteristics are encountered.

It should also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom. Although particular step sequencesare shown, described, and claimed, it should be understood that stepsmay be performed in any order, separated or combined unless otherwiseindicated and will still benefit from the present invention.

Although the different examples have specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents from another one of the examples.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

What is claimed is:
 1. An airfoil, comprising: pressure and suctionsides extending between a leading edge and a trailing edge, the airfoilhaving a camber line along an airfoil section that is equidistantbetween an exterior surface of the pressure and suction sides, thecamber line extends from a 0% camber position at the leading edge to a100% camber position at the trailing edge, wherein a ratio of a maximumthickness to an axial chord length is between 0.2 and 0.5, and whereinthe maximum thickness is located along the camber line between 13% and38% camber position; wherein the pressure and suction sides extend in aradial direction from a 0% span position to a 100% span position, andthe airfoil section is between 5% and 95% span; and wherein a thicknessof the airfoil as a percentage of the maximum thickness is between 28%and 76% at a 5% camber position.
 2. The airfoil according to claim 1,wherein the thickness of the airfoil as the percentage of the maximumthickness is between 4% and 20% at a 95% camber position.
 3. The airfoilaccording to claim 1, wherein the thickness of the airfoil as thepercentage of the maximum thickness over a camber position of theairfoil section is within a first and a second thickness trend line asshown in FIG.
 5. 4. The airfoil according to claim 3, wherein thepressure side has a radius of curvature divided by the axial chordlength over an axial chord position of the airfoil section within afirst and a second curvature trend line as shown in FIG.
 6. 5. Theairfoil according to claim 1, wherein the pressure side has a radius ofcurvature divided by the axial chord length over an axial chord positionof the airfoil section within a first and a second curvature trend lineas shown in FIG.
 6. 6. The airfoil according to claim 1, wherein theairfoil is a rotor airfoil.
 7. An airfoil comprising: pressure andsuction sides extending between a leading edge and a trailing edge, theairfoil having a camber line along an airfoil section that isequidistant between an exterior surface of the pressure and suctionsides, the camber line extends from a 0% camber position at the leadingedge to a 100% camber position at the trailing edge, wherein a ratio ofa maximum thickness to an axial chord length is between 0.2 and 0.5, andwherein the maximum thickness is located along the camber line between13% and 38% camber position; wherein the pressure and suction sidesextend in a radial direction from a 0% span position to a 100% spanposition, and the airfoil section is between 5% and 95% span; andwherein the pressure side has a radius of curvature divided by the axialchord length of between −1 and −3 at a 46% axial position.
 8. Theairfoil according to claim 7, wherein the pressure side has the radiusof curvature divided by the axial chord length of between 1.6 and 5.2 ata 5% axial position.
 9. The airfoil according to claim 8, wherein thepressure side has the radius of curvature divided by the axial chordlength of between −0.1 and −1.6 at a 95% axial position.
 10. The airfoilaccording to claim 7, wherein the airfoil is a stator airfoil.
 11. Theairfoil according to claim 7, wherein the airfoil is a rotor airfoil.12. A gas turbine engine comprising: a combustor section arrangedbetween a compressor section and a turbine section; an airfoil arrangedin one of the compressor section and the turbine section, the airfoilhaving pressure and suction sides extending between a leading edge and atrailing edge, the airfoil having a camber line along an airfoil sectionthat is equidistant between an exterior surface of the pressure andsuction sides, the camber line extends from a 0% camber position at theleading edge to a 100% camber position at the trailing edge, wherein aratio of a maximum thickness to an axial chord length is between 0.2 and0.5, wherein the maximum thickness is located along the camber linebetween 13% and 38% camber position; and wherein a thickness of theairfoil as a percentage of the maximum thickness is between 28% and 76%at a 5% camber position, and the thickness of the airfoil as thepercentage of the maximum thickness is between 4% and 20% at a 95%camber position.
 13. The gas turbine engine according to claim 12,wherein the airfoil is a stator airfoil.
 14. The gas turbine engineaccording to claim 12, wherein the airfoil is a rotor airfoil.
 15. Thegas turbine engine according to claim 12, wherein the airfoil isarranged in the turbine section.
 16. The gas turbine engine according toclaim 12, wherein the pressure side has a radius of curvature divided bythe axial chord length of between 1.6 and 5.2 at a 5% axial position,and the radius of curvature divided by the axial chord length of between−0.1 and −1.6 at a 95% axial position.
 17. The gas turbine engineaccording to claim 16, wherein the pressure side has the radius ofcurvature divided by the axial chord length of between −1 and −3 atabout a 46% axial position.
 18. The gas turbine engine according toclaim 12, wherein the thickness of the airfoil as the percentage of themaximum thickness over a camber position of the airfoil section iswithin a first and a second thickness trend line as shown in FIG.
 5. 19.The gas turbine engine according to claim 18, wherein the pressure sidehas a radius of curvature divided by the axial chord length over anaxial chord position within a first and a second curvature trend line asshown in FIG.
 6. 20. The gas turbine engine according to claim 12,wherein the pressure side has a radius of curvature divided by the axialchord length over an axial chord position within a first and a secondcurvature trend line as shown in FIG. 6.